Workers in the document-handling arts are well aware of transport mechanisms wherein documents are transported relatively continuously along a path past a fixed processing-station, there to be arrested, processed, and then advanced further along the path. An object hereof is to provide servo methods and means for precisely controlling document transport according to a preset velocity-profile in such cases.
In some such stations, print-hammers are arrayed; an example of such is disclosed in U.S. Pat. No. 4,510,619 to LeBrun et al. issued Apr. 9, 1985 and in U.S. Pat. No. 4,672,186 to Van Tyne issued June 9, 1987. These patents show an encoding system in which documents are continuously advanced past one or more banks of electromagnetically-activated print-hammers. Positioned on the other (non-hammer) side of the document are appropriately-encoded die means, presenting the (OCR or MICR) characters. Between the die and the document is an appropriate magnetic-ink ribbon which applies an ink-image of the die onto the document upon hammer impact. The system is "indexed" so that the required character is imprinted in the appropriate document-space based on timing the hammer strike with selected-die-presentation.
Workers are aware of certain disadvantages in present encoder arrangements; for instance, it is common for either or both the document and the ribbon to be moving during hammer-strike--and smudges or other imperfect imaging can result. Also, an extensive, unwieldy number of die sets and hammers must typically be provided to cover all possible combinations of symbols in all possible sequences (to be imprinted on the document). As will be described, the present invention overcomes these, and other, problems and disadvantages; e.g. by using a "print-drum" with normalized hammer-pressure and with paper-motion and ribbon-motion arrested; by using variable-energy hammer activation; by monitoring hammer movement/impact; by using print drum means with a special alignment mark; by using a servo system/sensor/software combination for controlled deceleration and alignment of a document; and by automatically correcting ribbon-wander.
Thus, it is an object hereof to address at least some of the foregoing needs and to provide one or several of the foregoing.